In the production of tubular steel couplers for joining opposing end portions of two concrete reinforcing rods, commonly referred to as “rebars”, for example, of the general type disclosed in U.S. Pat. Nos. 3,415,552, 3,551,999 and 5,664,902 which issued to the assignee of the present invention, it is common to purchase seamless steel tubing and cut the tubing into sections. The opposite end portions of the tubing sections may be formed with internal threads, for example, as disclosed in U.S. Pat. No. 3,415,552, or the opposite end portions of a tubing section maybe compressed or swaged radially inwardly onto the corresponding opposing end portions of the reinforcing bars, for example, as disclosed in U.S. Pat. No. 3,551,999. While the steel tubing usually has a generally cylindrical inner and outer surfaces, the inner surface may be machined with internal threads or with internal axially spaced circumferential teeth, as shown in the aforementioned patents. The cylindrical tubing may also be formed between dies to produce a tubular coupling body having non-cylindrical outer and/or inner surfaces, for example, as disclosed in above mentioned U.S. Pat. No. 5,664,902.
Since the cost of producing seamless steel tubing is substantially more than the cost of producing solid steel cylindrical bars or rods, tubular rebar coupler bodies have also been produced by machining sections of solid steel bar stock, preferably on a computer controlled lathe or machining center. A bore is first drilled within each solid rod section and then internal threads are machined within the bore. It is also known to machine one end portion of a solid coupler body to form an end portion of reduced diameter and on which external threads are then machined.
The end portion of the coupler body having the drilled bore is secured to an end portion of a concrete reinforcing bar by compressing or swaging the end portion radially with a mechanical or hydraulic press so that the coupler body positively grips the concrete reinforcing bar and provides the bar with an externally threaded end portion. The machined external and internal threads may be generally cylindrical or tapered, depending on the application of the rebar coupler. The primary disadvantage of machining solid steel bar stock or rod is the production of waste or scrap material which adds significantly to the cost of producing the rebar couplers.